1. Field of the Invention
The present invention relates to a rotary shaft sealing system and, in particular, to a flinger device for preventing the ingress of foreign matter to a side of a bearing surface between a rotary shaft seal and its associate shaft.
Housing-mounted rubber-lipped seals are a generally efficient form of sealing rotating shafts in order to prevent oil leaking from internal combustion engines. These seals usually comprise a circular metal housing into which is moulded a rubber seal having two lips, an inner shaft-contacting and spring-assisted lip and an outer non-contacting, non-spring-assisted, lip.
The seal is fitted to a shaft in the engine so that an inner lip faces an oil (lubricated) side of the shaft to contain the oil within the engine and an outer lip faces away from the engine to provide some protection from the ingress of foreign matter to the vicinity of the inner lip and the moving (bearing) surface against which it seals. A surface of the inner lip presses against a smooth peripheral surface of the rotating shaft and may have a scroll moulded into its surface to cause oil to wind towards the engine side of the seal as the shaft rotates. It is commonplace for a seal of this type to be fitted at each end of the crankshaft.
The front end of an engine usually benefits from a labyrinth sealing system provided by the shaped rear face of the crankshaft-mounted pulley closely following that of the adjacent front face of the engine. This, and the centrifugal effect of the rotating pulley on the surrounding air, assists in directing dirt, which can be in dry, airborne form or may be thrown up as a wet slurry, away from the front oil seal. Front seal wear from abrasives is therefore not generally a problem.
In dirty operating environments, a crankshaft oil seal fitted at the rear end of an engine may suffer from dirt ingress to a greater extent than a seal fitted at the front end. This is particularly true where the engine is used as an open power unit and the rear end does not have the protection of a flywheel housing or a clutch housing. In these situations, abrasive foreign matter can access the seal to crankshaft contact area and wear both the seal and the corresponding surface of the crankshaft. The wear to the crankshaft may be exacerbated by abrasive particles becoming embedded in the relatively soft rubber of the seal.
A known method of protecting the crankshaft and other shaft seals is to provide a `flinger` device adjacent the `dirty` side of the seal which rotates with the shaft. The flinger device is generally circular with a diameter exceeding that of the seal and it serves to throw out abrasives, by centrifugal action, in a similar manner to the crankshaft pulley at the front end of the crankshaft.
There are disadvantages with the use of flinger devices. Firstly, flinger devices which fit closely adjacent to the seal but are non-contacting with surrounding surfaces, do not fully protect the seal and bearing surface from airborne abrasive foreign matter when the engine is running. Nor do they protect the seal when the engine is not operating at which time abrasive dirts or slurries can run down the engine block, etc, into the vicinity of the crankshaft/seal bearing surface and become trapped, thus causing abrasion when the engine is operated again.
2. Descriptive of the Related Art
The problem of crankshaft rear seal wear in dirty operating environments has been previously discussed. On page 58 of the publication `Design News` of Dec. 2, 1996 is disclosed an apparatus for protecting a crankshaft rear oil seal from external contamination. This apparatus comprises a preformed metal sleeve carrying an integral rubber lip. The apparatus is pressed onto the flange of the crankshaft and is therefore caused to correspondingly rotate during engine operation. The rubber lip part of the apparatus is in contact with an inner surface of the seal retaining housing and has the function of isolating the seal from sources of external contamination.
The seal protecting apparatus described in the aforementioned publication has the disadvantage that the rubber lip is itself directly exposed to abrasives in foreign matter and may suffer wear and embedding of abrasives in the relatively soft material of the lip, thus becoming progressively less effective.